This invention relates to offshore, deep water structures, particularly of the mobile or jack-up type, for instance, for oil well drilling, testing, or production operations.
The utility of conventional structures of this type is limited to going onto and off locations in relatively calm weather conditions and low wave heights which may exist for only short time periods and to relatively shallow waters with bottom conditions more or less even and consistent, and because of their great cost. This is due in part to the relatively high resistance they offer to environmental forces in rough waters resulting, in part, from the turbulence producing teeth or holes or other anomalies provided along the legs for use in manipulating the legs.
Slanting of the legs has marked advantages, but, heretofore, slant leg platforms have not been wholly satisfactory, particularly in deep, rough waters, where they would be most advantageous. This is due to the impossibility of maintaining the legs at substantially uniform angles; the great danger is that less than all the legs may engage the bottom during descent and thereby be subjected to excessive and dangerous bending and twisting forces. Leg operating mechanisms current in offshore drilling rigs power the legs up and down at relatively slow rates. Thus, if the hull should be lifted or rocked just as the legs approach the bottom, a leg mechanically attached to the platform may be lifted free of the bottom even though leg lowering continues, so that the affected leg, at its next descent, may strike the bottom at a different point thus changing the leg angle, possibly with destructive results. As the hull is lifted in and from the water, the leg angularity maintaining means must be released, but when such means is released before the legs have arrived at their final location on or in the ocean bottom, a lifted leg, as by wave action, will inevitably pivot by gravity action toward vertical, again disturbing the support symmetry. Moreover, in case the operator should not release the angle maintaining means together and at the correct moment of contact with the bottom, simultaneously with lifting of the hull, a difficult task, destruction of the leg attaching mechanism or damage to the leg could result.